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(11) | EP 0 007 212 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Protective control system for vehicle starter and electrical systems |
| (57) A protective control system for the starter system of an engine cranked by a starter
motor 32 includes a frequency selective logic 38 responsive to engine RPM to automatically
open the starter relay26 above a predetermined frequency, to prevent cranking of the
engine above the corresponding engine RPM, and the frequency selective logic 38 includes
a hysteresis network to prevent re-closing of the starter relay, and re-cranking of
the engine, until engine RPM drops to a lower level. |
[0002] Protective systems for starter mechanisms in motor vehicles are known in the art. Protection is desirable in order to prevent damage which may otherwise occur if the starter is overrun, or re-energized after the engine is running. Starter protector or lock-out systems typically sense some function of engine RPM during the starter sequence and automatically remove electrical power to the starter motor when the engine attains an adequate RPM level to be running. Starter disconnect circuits are known which respond to intake manifold vacuum, oil pressure, frequency of an AC generator voltage, etc., to disable the starter at a predetermined engine RPM.
[0003] Starter control systems are also known in which after starter lock-out, the relay is maintained open until the engine spe<d falls to practically zero. Other starter protectors are known which require manual intervention for restart. Mechanically sequenced starter switches are also known.
[0004] The present invention provides a protective control system for the starter system of an engine which is cranked by a starter motor, comprising a starter relay in circuit with said starter motor, and frequency selective means responsive to engine RPM to automatically open said starter relay means above a predetermined threshold set frequency corresponding to a designated RPM level, to prevent cranking of said engine thereabove, said frequency selective means including hysteresis means to prevent re-closing of said starter relay means until engine RPM drops to a lower level corresponding to a reset frequency less than said threshold set frequency, whereby to prevent re-cranking of said engine until engine RPM drops to said lower level.
[0005] An embodiment of the invention to be described herein is an improved protective control system for vehicle starter systems which senses alternator frequency as a measure of engine RPM and automatically de-energizes the starter relay above a given threshold frequency and in which such frequency selective circuit includes a hysteresis network also responsive to alternator frequency to prevent subsequent re-energization of the starter until a reduced engine RPM.
[0006] In the embodiment to be described, the control system is combined with an electrical system control having a master switch for connecting the vehicle battery to the starter system and to the electrical system of the vehicle and having signal detection means also responsive to the alternator to prevent disconnection of the battery while the engine is running even if the master switch is subsequently opened.
[0007] Said embodiment comprises a compact module easily added to existing starter and electrical systems. A frequency selective circuit is responsive to alternator frequency for not only locking-out the starter at a selected threshold frequency but also including a hysteresis network for preventing re-energization of the starter above a lower selected frequency. Both the threshold and the lower selected frequencies are adjustable. Excellent thermal stability of the threshold frequency lock-out set point is exhibited. A wide range of frequency hysteresis is achieved. An integrated circuit is utilized for threshold frequency selection. An add-on hysteresis network affords a wider range of hysteresis, and thus a substantially lower reset frequency point, than available solely from a resistor connection between a designated two of the integrated circuit's pins.
[0008] In the embodiment to be described, a voltage regulation circuit is provided for assuring a stable supply voltage to the remainder of the protective control. An input waveshaping circuit compensates for the poor waveform shape, variable amplitude, and associated electrical extraneous noise in the AC voltage signal from the alternator. Protection for reverse polarity battery connection is provided.
[0009] Said embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:
Figure 1 is a block circuit diagram illustrating a protective control module according to the present invention and showing its application; and
Figure 2 is a circuit diagram of the protective control module of Figure 1.
[0010] A general functional description will be given first referring to Figure 1, followed by a detailed description referring to Figure 2.
[0011] There is shown in Figure 1 a protective control module outlined by a box 22, for use in a motor vehicle. The module includes a main relay 24 and a starter relay 26. The main relay is used to connect the vehicle battery 28 to the vehicle electrical system, generally designated 30. The starter relay is used to control the engine starter motor 32, and is connected to the starter solenoid 34.
[0012] The main relay and the starter relay are each controlled by respective electronic logic circuits 36 and 38 which are responsive to the AC voltage output signal of alternator 40. The alternator is driven by the engine, and thus the presence of an output signal from the alternator indicates that the engine is running, and the frequency of the AC voltage signal is a function of engine RPM.
[0013] Logic circuit 36 permits energization of main relay 24 when master switch 42 is manually closed by the driver, enabling current to flow to coil 24a which then pulls in armature 24b downwardly to complete a circuit from battery 28 to electrical system 30. Logic circuit 36 includes signal detection means, to be more fully described hereinafter, which senses the presence of a signal fro:n alternator 40 and will hold the main relay closed even if the master switch is subsequently opened. This prevents disconnection of battery 28 from electrical system 30 while the engine is running. When no alternator signal is present, master switch 42 can open as well as close main relay 24.
[0014] Logic circuit 38 permits energization of starter relay 26 when main relay 24 is closed and starter switch 44 is manually closed by the driver enabling current to flow to coil 26a which then pulls in armature 26b downwardly to complete a circuit from battery 28 turough main relay 24 and through starter relay 26 to starting motor solenoid 34, and hence enabling cranking of the engine by starting motor 32. Logic circuit 38 includes frequency selective means, to be more fully described hereinafter, which senses the frequency of the AC output signal from alternator 40 and responds to a predetermined set threshold cut-out frequency by automatically terminating current flow to coil 26a thus de-energizing starter relay 26 and breaking the circuit to solenoid 34, hence disengaging the starter. 1he set threshold cut-out frequency corresponds to a designated engine RPM beyond which the engine should not be cranked by starter motor 32. The frequency selective means of logic circuit 38 also includes hysteresis means which prevents subsequent re-energization of starter relay 26 until the AC signal frequency drops to a substantially lower reset cut-in frequency, preferably near zero, so that the engine cannot be cranked again until its RPM is low enough that the solenoid drive teeth, flywheel teeth, etc. will not be damaged.
[0015] The above and other functions are accomplished by the embodiment shown in Figure 2 which is a circuit diagram of module 22 of Figure 1. The module has six connection points or terminals, identified A to F in Figure 1. These connection points are correspondingly lettered in Figure 2.
[0016] The particular module disclosed was specifically designed for use in military vehicles, though the invention is of course not limited thereto. The module is compact, measuring 7 1/2 inches (19.05 cm) long by 3 1/2 inches (8.89 cm) wide by 3 1/2 inches (8.89 cm) high, and is an easy to install component. Terminal A is connected through master switch 42 to the positive side of battery 28. Terminal C is connected to the positive side of battery 28. Terminal D is connected to alternator 40 and to the vehicle electrical system 30 in Figure 1. Starter switch 44 is connected between terminals D and E. Terminal B is connected to starting motor solenoid 34. Terminal F is connected to the alternator to sense the AC output signal thereof; this AC signal is typically available as a special tap internal to the alternator on the AC side of the rectifier diodes.
[0018] Dashed box 46 outlines a voltage regulation circuit comprising the combination of dropping resistor 48 and zener diode 50 used in the particular disclosed embodiment to drop the military vehicle 24 volt DC power down to a regulated 12 volt DC level supply for the precision frequency selective circuitry, to be described hereinafter.
[0019] Dashed box 52 outlines an input waveshaping circuit. The AC signal supplied by the alternator does not have a clean waveshape, and it varies in magnitude, particularly during the starting interval with which the present invention is concerned. A resistor 54 limits current to the base of an NPN transistor 56 and also forms an RC noise filter with a capacitor 58 connected across the base and emitter of transistor 56. The alternator signal is fed via terminal F through this network to the base of transistor 56 which is switched on and off by the signal. The collector of transistor 56 switches on and off (low and high) on the leading and trailing edges of the signal to the base, providing a pulse shaped signal of constant amplitude which is more suitable to be fed to the frequency selective circuitry, to be described hereinafter. Resistor 60 is connected in parallel with capacitor 58 across the transistor base-emitter to provide a base to emitter return path to aid turn-off. Resistor 62 is a collector load, or pull-up, resistor and is connected between the transistor collector and voltage regulation circuit 46. Capacitor 64 and resistor 66 provide coupling from the transistor collector signal to the frequency selective circuit.
[0020] Dashed box 68 outlines a frequency selective circuit. This circuit includes 3344 type integrated circuit (Motorola Corp. MC 3344L), designated by the reference character 70. The same pin designations assigned to a 3344 type integrated circuit are used in Figure 2, to facilitate clarity of the description to follow. The other components in frequency selective circuit 68 will be identified in the continuing description.
[0021] The pulse waveform from the collector of transistor 56 is fed to input pin 11 of component 70, and an output DC signal is derived at pin 3. Pin 3 is high or ON as long as the incoming frequency at pin 11 is below a predetermined set point or threshold frequency, which in this particular embodiment is 127 Hz. As the engine is started and its RPM's increase to a running or idling level, the frequency of the sensed alternator signal reaches 127 Hz at which point pin 3 now goes low or OFF, removing bias to the base of transistor 72 which in turn causes disengagement of starter relay 26, to be more fully described hereinafter. The frequency of the switch point is determined by the values of resistors 74 and 76 and capacitor 78. A stable metal glaze resistor is used for 74 and a polycarbonate capacitor for 78 to provide excellent frequency stability for the cut-out switch point of 127 Hz. This switch point remained within ± 2Hz over the temperature range -65°F to +250°F (-54°C to 121oC). Component 70 itself is very stable but is at the mercy of the external threshold frequency determining elements.
[0022] A frequency hysteresis network, outlined in dashed box 80, is added in frequency selective circuit 68 such that once the trip out frequency at pin 11 has been attained or exceeded, the input frequency at pin 11 must now drop down substantially below said threshold trip out frequency before the starter relay can be re-energized (by pin 3 going back high), thus assuring starter lock-out until the engine is essentially stopped. The hysteresis drops the reset frequency to below 10 Hz in_, this particular embodiment. This is accomplished by transistor 82 in conjunction with resistors 84 and 86 and capacitor 88, and a switching signal from pin 5 of component 70. When the frequency of the input signal to pin 11 is below the threshold trip frequency, 127 Hz, pin 5 is low or OFF, but when the input signal on pin 11 reaches 127 Hz, pin 5 switches high (the opposite or complement of output pin 3). When pin 5 toggles high, the base of transistor 82 is biased on through resistor 84. The collector of transistor 82 goes low, effectively grounding one side of capacitor 88, whereby the latter now is in effect in parallel with capacitor 78. (When the collector of transistor 82 is high, capacitor 88 is merely floated). The addition of capacitor 88 in the frequency determining network of component 70 drops the switching frequency down to below 10 Hz. Once below this reset point, the threshold trip frequency will again recover to 127 Hz, allowing a normal restart of the engine. It is thus seen that when the input frequency at pin 11 reaches 127 Hz, pin 3 toggles low to disengage the starter and pin 5 toggles high to drop the reset frequency down to below 10 Hz. Pin 3 remains low until the input frequency at pin 11 decreases to less than 10 Hz, at which point pin 3 toggles back high (pin 5 goes low) to thus bias on transistor 72 whereby starter relay 26 may be re-energized and the engine cranked again.
[0023] A type 3344 integrated circuit, component 70, has provisions for obtaining hysteresis of input frequency by merely adding a resistor 90 between pins 10 and 12, but the range between initial and reset frequency set points, without adversely affecting circuit operation, was not as wide as preferred. Thus the hysteresis network 80 with transistor 82 switching in capacitor 88 was added, and was very effective. Since the low, or reset, frequency point is not critical compared to 4 the initial threshold set frequency point, the requirements for capacitor 88 stability are not as great as for capacitor 78.
[0024] Other components in frequency selective circuit 68 include resistor 92 which limits the output current from pin 3 to the base of transistor 72, and capacitor 94 which is part of an additional integrator network used in the operation of integrated circuit 70.
[0025] Dashed box 96 outlines a starter relay drive circuit. The output switching signal from pin 3 of component 70 is supplied to the base of a darlington power transistor 72 which functions as an amplifier switch for starter relay coil 26a. When starter switch 44, Figure 1, is closed, 24 volts DC is supplied to terminal E, Figure 2, and starter relay 26 will be energized, whereby the engine is cranked. When the engine attains a predetermined RPM level, as indicated by the alternator supplying 127 Hz to the circuit at terminal F, the starter relay will be de-energized by transistor 72 turning off in response to pin 3 going low. The starter relay 26 will remain de-energized, even if starter switch 44 is held closed or re-closed, until the alternator signal drops below 10 Hz, whereby the engine cannot be cranked again until it has essentially stopped.
[0026] Other components in starter relay drive circuit 96 include diode 98 and zener diode 100 which form a transient suppressor to prevent relay coil 26a from developing high reverse voltages or back emf during turn off switching. Resistor 102 is a base to emitter return resistor to aid in the turn-off of transistor 72. Diode 104 provides reverse polarity protection to starter relay drive circuit 96. Diode 104 actually is redundant because additional reverse polarity protection is provided (by diode 120) in the main relay 24 switching circuit which, if not closed, will not permit power to be applied to starter switch 44, to be more fully described hereinafter.
[0027] Dashed box 108 outlines a signal detector circuit, and dashed box 110 outlines a main relay driver circuit. These circuits provide the interlock action that prevents opening or de-energizing of main relay 24, which connects the battery to the electrical system, while the engine is running.
[0028] Signal detector circuit 108 rectifies and filters the AC alternator signal, supplied to terminal F, through diode 112 and capacitor 114 and forms a DC voltage to bias ON darlington power transistor 116. Normally, when the engine is not running, master switch 42 will supply battery power to terminal A and will thus energize main relay 24 by supplying bias to the base of transistor 116 through resistor 118, and supplying coil bias through diode 120. Conduction of transistor 116 completes a circuit from terminal A through main relay coil 24a through transistor 116 to ground, whereby master switch 42 can thus turn main relay 24 on and off. However, once the engine is running and the alternator signal correspondingly supplied to signal detector circuit 108, transistor 116 will be based ON even if master switch 42 is opened; in such case, coil 24a bias is supplied from terminal D through diode 106. Consequently,main relay 24 will remain closed until the alternator signal ceases, i.e. the engine stops. In the particular application of the preferred embodiment, the engine is not supposed to be stopped by the master switch, but by a fuel shutoff valve commonly used in diesel engined vehicles.
[0029] Diode 120 is the primary reverse polarity protection in the system; If the battery is connected in reverse, the electrical system cannot be connected because main relay 24 cannot be initially closed.
[0030] Diode 122 and zener diode 124 provide coil suppression for the main relay. Resistor 126 limits current from the detector circuit 108 to the base of transistor 116. Resistor 128 is a base to emitter return resistor to aid in turning off transistor 116. Resistor 130 is used to lower the input impedance of the circuit at point F.
Operation
[0032] The vehicle operator first closes master switch 42, Figure 1, thus supplying battery power to terminal A. If the battery polarity is correct, main relay 24 will close due to the bias to coil 24a through diode 120 and transistor 116, Figure 2. If the battery polarity is reversed, main relay 24 will not close because diode 120 is then blocking and prevents application of power to coil 24a; no circuit damage occurs because the electrical system cannot be connected, nor can starter relay 26 be energized.
[0033] With correct battery polarity and main relay 24 closed, battery 28 is tied into the vehicle electrical system by armature 24b closing the contacts between terminals C and D, Figure 1. At this time master switch 42 has full control of main relay 24 and can open the latter if desired.
[0034] With the electrical system now energized, the operator can start the engine by closing starter switch 44, Figure 1, supplying power from terminal U to terminal E. Starter relay 26 will now be energized because transistor 72, Figure 2, is biased ON by a signal from output pin 3 of component 70 which in turn has sensed at input pin 11 that no signal yet exists from the alternator at terminal F. The engine will now be cranked by starter motor 32, Figure 1, because of the energization of solenoid 34 enabled by the completed circuit therethrough from closed starter relay 26.
[0035] As the engine begins to pick up speed, its RPM level increases such that alternator 40, Figure 1, will generate a signal at its AC internal tap, which AC signal is fed to terminal F on control module 22. The AC signal frequency is proportional to engine RPM, and when the frequency reaches a predetermined set point value, here 127 Hz, frequency selective circuit 38 in Figure 1, 68 in Figure 2, ceases bias to starter relay drive circuit 96, thus dropping out or opening starter relay 26 (unless of course the starter relay has already been opened by the operator's opening of starter switch 44). The starter function is now locked out and starter switch 44 is ineffective until the alternator's AC signal frequency is very low due to the hysteresis provided in frequency selective circuit 68 by frequency hysteresis network 80, Figure 2, after trip out. The low level reset point in this case is 10 Hz, whereby the engine must be essentially stopped before it can be re- cranked.
[0036] While the engine is running and the alternator signal is supplied to terminal F of the module, the master switch 42 can be opened but the main relay 24 will remain closed due to the signal detector circuit 108, Figure 2, maintaining bias on main relay driver circuit 110. Main relay 24 can only be opened when the engine RPM is very low such that the alternator signal ceases.
1. A protective control system for the starter system of an engine which is cranked
by a starter motor (32), comprising a starter relay (26) in circuit with said starter
motor, characterised by frequency selective means (68) responsive to engine RPM to
automatically open said starter relay above a predetermined threshold set frequency
corresponding to a designated RPM level, to prevent cranking of said engine thereabove,
said frequency selective means including hysteresis means (80) to prevent re-closing
of said starter relay means until engine RPM drops to a lower level corresponding
to a reset frequency less than said threshold set frequency, whereby to prevent re-cranking
of said engine until engine RPM drops to said lower level.
2. A control system according to claim 1, comprising a transducer (40) responsive
to engine speed to produce a signal whose frequency corresponds to engine RPM, said
frequency selective means having an input for receiving said transducer signal and
an output controlling said starter relay, said transducer signal, upon reaching said
threshold set frequency, causing said output to switch states and also activating
said hysteresis means to lower the frequency value necessary to cause switching of
said output back to its original state.
3. A control system according to claim 2, wherein said transducer comprises an AC
signal generator, and further comprising input waveshaping means (52) for receiving
the AC signal and delivering a clean waveshape signal to said input of said frequency
selective means.
4. A control system according to claim 2 or 3, wherein said frequency selective means
comprises a' programmable frequency switch (70) having an input (11) receiving said transducer
signal and a pair of opposite state outputs (3,5) one of which is connected to said
starter relay the other of which is connected to said hysteresis network, such that
when the frequency of said transducer signal at said input (11) reaches said threshold
value, said outputs switch states such that said one output (3) causes opening of
said starter relay and said other output (5) causes said hysteresis network to lower
the value of said threshold frequency down to said reset frequency.
5. A control system according to claim 4, wherein said hysteresis network comprises
a capacitor (88) which is floated when the other of said outputs (5) is in the first
mentioned of its states, and which is connected in circuit with said frequency switch
(70) when said other (5) of said outputs switches to its second mentioned state. .
6. A control system according to claim 5, wherein said hysteresis network comprises
a transistor (82) which is biased into conduction by said second state of said other
output (5) to complete said circuit through said capacitor.
7. A control system according to claim 5 or 6, wherein said frequency selective means
comprises a second capacitor (78) connected to another input (10) of said frequency
switch for selecting the value of said threshold set frequency, said first capacitor
(88) being connected in parallel with said second capacitor (78) when said other output
(5) is in said second state, said parallel combination of said capacitors determining
the value of said reset frequency.
8. A control system according to any one of claims 4 to 7, wherein said one output
(3) of said frequency switch is high until the frequency of said transducer signal
reaches said threshold set frequency whereafter said one output switches low and remains
low until the frequency of said transducer signal drops below said reset frequency
due to said hysteresis network, and further comprising a transistor (72) in circuit
with said starter relay and biased into conduction by said one output (3) when in
said high state to enable completion of a circuit through said starter relay whereby
the latter may be closed to permit energization of said starter motor and cranking
of said engine.
9. A control system according to any one of claims 3 to 8, wherein said transducer
(40) comprises an alternator driven by said engine, and wherein said input waveshaping
means (52) comprises a transistor (56) biased by the AC alternator signal to abruptly
switch ON* and OFF on leading and trailing edges of said AC signal, one of the emitter
and collector of said transistor thus switching low and high and connected to said
input of said frequency selective means for delivering a clean pulse shape signal
thereto.
10. A control system as claimed in any preceding claim further comprising a main relay
(24) between a battery (28) and a main electrical system (30) of the vehicle, said
starter relay (26) being between said main relay and said starter motor (32), a master
switch (MS) in circuit with said main relay, a starter switch (44) in circuit with
said starter relay, electronic logic (110) for said main relay to permit energization
of said main relay when said master switch is closed, means to sense engine RPM and
maintain said main relay closed even if said master switch is subsequently opened
whereby to prevent disconnection of said battery from said electrical system when
said engine is running, energization of said starter relay being permitted, after
said main relay is closed, when said starter switch is closed, to thus enable energization
of said starter motor and cranking of said engine.
11. A control system according to claim 10 appended to claim 2, wherein said electronic
logic for said main relay comprises signal detection means (108) for detecting the
presence of a signal from said transducer and for delivering said signal to a transistor
(116) in circuit with said main relay to bias said transistor (116) into conduction
to enable completion of a circuit through said main relay.
12. A control system according to claim 11 wherein closure of said master switch connects
said battery to the base of said transistor (116) to thus bias said transistor into
conduction and hence energize said main relay.
13. A control system according to claim 10, comprising a diode (120) connected between
said master switch and said main relay tn provide reverse polarity protection by preventing
energization of said main relay by said battery if the latter is connected with improper
polarity.
14. A control system according to claim 10, comprising a pre-assembled module which
may be added to the existing circuitry of a vehicle having an alternator driven by
the vehicle's engine, said module having a first terminal (A) connectable to said
battery through said master switch, said first terminal being connected internally
of said module to said electronic logic for said main relay, said module having a
second terminal (B) connectable to said starter motor, said second terminal being
connected internally of said module to one side of said starter relay, said module
having a third terminal (C) connectable to said battery in parallel with the series
combination of said master switch and said first terminal, said third terminal being
connected internally of said module to one side of said main relay, said module having
a fourth terminal (D) connectable to said electrical system, said fourth terminal
being connected internally of said module to the other side of said main relay, said
module having a fifth terminal (E) connectable to said fourth terminal through said
starter switch, said fifth terminal being connected internally of said module to electronic
logic for said starter relay, said module having a sixth terminal (F) connectable
to said alternator for feeding to said module an AC signal having a frequency corresponding
to engine RPM, said sixth terminal being connected internally of said module to said
electronic logic for said starter relay and to said electronic logic for said main
relay.